std::declare_reachable (3) - Linux Manuals
Defined in header <memory>
void declare_reachable( void* p ); (since C++11)
Declares the object referenced by the pointer p reachable. Reachable objects will not be deleted by the garbage collector or considered to be a leak by a leak detector even if all pointers to it are destroyed. An object may be declared reachable multiple times, in which case multiple calls to std::undeclare_reachable would be needed to remove this property. For example, a XOR_linked_list needs to declare its nodes reachable if the implementation has garbage collection enabled.
p - a safely-derived pointer or a null pointer
May throw std::bad_alloc if the system cannot allocate memory required to track reachable objects.
This section is incomplete
Reason: no example
undeclare_reachable declares that an object can be recycled